Is there a way to visually determine whether refraction or interference is the cause of the iridescent effect observed in rainbows, oil films/bubbles, insect shells/wings, cds/dvds, etc.? This question arose from when I was looking at thin films of minerals through a microscope. The slide was illuminated with unpolarized white light. The mineral had a iridescent, "rainbowing" appearance that would change with rotation of the slide. During the lecture, the professor seemed to interchange differential indices of refraction and interference as causes for the effect. This confused me, because I thought refraction and interference were two separate subjects. I understand that it is refraction occurring in a rainbow that separates wavelengths into visible bands, and that interference from light reflecting off of diffraction grating causes different wavelengths to appear at different angles in the case of cds and dvds. Are the processes of refraction and interference mutually exclusive, or do they both contribute to the effects observed in the phenomena mentioned above? Any help will be greatly appreciated.